The applicant, CIMV, is a company specializing in the treatment and economic use of lignocellulosic vegetable raw material.
In this regard, the applicant has filed and is the proprietor of various patent applications and patents relating to a process for producing paper pulp, lignins, sugars and acetic acid by fractionation of lignocellulosic vegetable material in a formic acid/acetic acid medium (WO-A1-00/68494).
The applicant is also the proprietor of patent applications and/or patents relating to a process for pretreating a lignocellulosic vegetable material with a view to producing bioethanol (WO-A2-2010/006840).
Such a pretreatment process makes it possible in particular to obtain, from the lignocellulosic vegetable raw material (LVRM), under economic industrial conditions, firstly a substrate made up essentially of defibred cellulose exhibiting optimum conditions for its subsequent enzymatic hydrolysis, and a second substrate made up of sugar molasses originating from hemicelluloses of which the hydrolysates are devoid of furfural.
The applicant has therefore already proposed a process for producing bioethanol from a lignocellulosic vegetable raw material, comprising the successive steps of pretreatment of the LVRM, of enzymatic hydrolysis of the pretreated material and of alcoholic fermentation of the products resulting from the hydrolysis step.
The applicant has in particular proposed a process for producing bioethanol from a lignocellulosic vegetable raw material, comprising the successive steps of:                a) pretreatment of the lignocellulosic vegetable raw material in order to separate the cellulose, the hemicelluloses and the lignins contained in this lignocellulosic vegetable raw material, the pretreatment comprising the following successive steps consisting in:        (i) destructuring the lignocellulosic vegetable raw material by placing it in the presence of a mixture containing formic acid and water, at a reaction temperature between 95° C. and 110° C.;        (ii) then, at atmospheric pressure and prior to any hydrolysis then fermentation action, in separating:        on the one hand, the solid phase mainly consisting of said cellulose capable of then being hydrolysed and fermented for the production of bioethanol;        and on the other hand, the liquid phase, containing in particular in a solution of water, the formic acid, the lignins and the hemicelluloses;        b) enzymatic hydrolysis of said solid phase;        c) alcoholic fermentation of the products resulting from said hydrolysis step, which are capable of being fermented for the production of bioethanol.        
This process is in particular described in detail in document EP-2 235 254 (WO-A1-2009/092749), to the content of which reference may be made and which is incorporated herein by way of reference.
This process proposes an approach that is radically different from that of the prior art, by carrying out a separation of the three biopolymers by solvolysis in an acid/water medium, which makes it possible to separate linear, non-recombined, low-molecular-weight lignins with a high added value, prior to any action of hydrolysis then of fermentation of the cellulose and of the hemicelluloses.
This process, which makes it possible to obtain industrial performance levels regardless of the nature of the plants used, and which is therefore particularly advantageous in the case of annual plants for opening the way to a new economic use, in particular in the case of cereal straws and sugarcane bagasse or sugar sorghum bagasse, said economic use adding to that already proposed by the applicant in International Application WO-A1-00/68494 which relates to a process for producing paper pulp, lignins, sugars and acetic acid by fractionation of lignocellulosic vegetable material in a formic acid/acetic acid medium.
These inventions (CIMV processes) are aimed at improving the industrial conditions for the production of ethanol or bioethanol from LVRM, and in particular the hydrolysis of cellulose to give fermentable sugars.
Generally and in a known manner, the processes for producing bioethanol from LVRM take into account several parameters.
Among these parameters, it has in particular been identified that lignin can be an enzyme inhibitor and that the lignocellulosic matrix must be pretreated in order to make the cellulose and the hemicelluloses hydrolysable.
By virtue of their chemical composition, lignin polymers are insoluble and highly reactive.
As a result, the presence of lignins reinforces the cellulose-hemicellulose network, and they hinder the penetration and the action of enzymes, requiring the presence of water.
Enzymatic hydrolysis of cellulose is a recommended approach for obtaining fermentable sugars for various reasons, and in particular because the results of economic evaluations are in favour of enzymatic hydrolysis, when it is compared with chemical hydrolysis.
Furthermore, enzymatic hydrolysis generates few effluents to be treated and no corrosion problems.
The actual enzymatic hydrolysis is carried out by simply bringing the pretreated vegetable raw material into contact with an enzymatic solution, while ensuring that the suspension is homogeneous and that optimum conditions are maintained, said conditions being, for example for T. reesei cellulases, a temperature between 45° C. and 50° C. and a pH of about 4.8.
The enzyme action time depends on the amount of enzymes that is used and on the specific activity of the enzymes.
During the enzymatic hydrolysis, the reducing sugars are essentially released in the form of glucose.
The enzymes involved in cellulose degradation, which are commonly called cellulases, are of various types and of various origins and they are characterized in particular by their activity.
The cost of the cellulases is relatively high and constitutes a factor often estimated to be the most expensive in the production of bioethanol from LVRM.
As a result, important efforts have been made to determine the mechanism of enzymatic hydrolysis with a view to improving it, it being a complex process of the action of soluble proteins on an insoluble and “refractory” substrate.
Another parameter of the efficiency and cost-effectiveness of an enzymatic hydrolysis process is the hydrolysis time, which can be relatively long, from 48 to 72 h.
Once the cellulose has been hydrolysed to glucose by enzymatic hydrolysis, the glucose is fermented in the same way as, for example, the glucose resulting from starch.
Known problems specific to the use of LVRM as initial substrate remain, such as the possible presence of toxic compounds and inhibitors resulting from the hemicelluloses and the lignin, and also the possibility of carrying out the enzymatic hydrolysis and the fermentation in a single step.
The inhibitors present in the hydrolysates originate from the degradation of the sugars (to furfural), of groups present in the hemicelluloses, of the lignin.
The presence of the inhibitors depends on the nature of the LVRM and on the conditions for its pretreatment.
In addition to the inhibition of the enzymes by furfural, combined effects of the various inhibitors have been noted.
As regards the simultaneous fermentation and hydrolysis according to the “SSF” (“Simultaneous Saccharification and Fermentation”) process which consists in carrying out the enzymatic hydrolysis and the ethanolic fermentation in a single step, the main advantages thereof are the decrease in investments by eliminating the operations necessary for the enzymatic hydrolysis carried out beforehand, and the absence of cellulase inhibition by glucose, which is consumed by the fermentative microorganisms as it appears.
This results in an increase in the levels and rates of hydrolysis and in the overall ethanol or bioethanol productivities.
Moreover, the risks of microbial contamination of the glucose-rich hydrolysate are reduced.
However, it has become apparent that the gains provided by the SSF process, in particular from the economic point of view, require certain aspects to be optimized, in particular the initial dry matter concentration in order to obtain high concentrations of ethanol.